I am working on a Type 99 rifle for the Japanese which is modeled after the Kar 98. I edited the weapon properties and created a new class of ammunition, but cannot drag and drop the ammo to the weapon so that it would show in a result of all weapons using that ammo. In the game the associated munitions are the 7.92mm of the Kar 98, and they do decrease when the IJA infantry company is engaged (they do fire back with my Type 99, but using Kar 98 ammo).

The field in the weapon data screen is grayed out and I cannot drag the ammo there: